Wireless communication is rapidly growing. For example, peripheral devices and human interface devices (HIDs) are increasingly utilizing wireless communication, such as Bluetooth, to communicate with a host computer.
Bluetooth (BT) is a wireless protocol and thus requires a radio transmitter and radio receiver. Bluetooth integrated circuits (ICs) and other wireless chips with radios integrated on a single silicon die often incorporate temperature sensors used to calibrate radio circuits across temperature variations. Other wireless protocols, such as those typically operating in the 27 MHz frequency band, may operate in one direction only, in which case only a radio transmitter is required.
In some applications in which the radio is used with a high duty cycle IC, the temperature of the die increases from the ambient temperature due to the high duty cycle of the IC. Hence, while the temperature measurement from the temperature sensor may be good for calibrating the radio circuits, it is not an accurate measurement of the ambient temperature. Furthermore, the radio is often embedded in a product (e.g., inside a laptop case or automobile) which can have an internal temperature that is significantly higher than ambient temperature.
However, in a Bluetooth HID, the radio is typically used at a low duty cycle, typically less than 10%. Hence, the die temperature is not significantly raised above the ambient temperature. Furthermore, the HID is typically separated from the host device and usually contains no other circuitry which would raise its internal temperature.
Therefore, in a BT HID, the die temperature is closely tracking the ambient temperature. The present invention takes advantage of the above characteristics of a BT HID to integrate a temperature sensor in the HID that substantially indicates the ambient room temperature.